University of Mississippi University, Mississippi, United States
Background/Question/Methods
An important goal of oak ecosystem restoration projects is to determine whether restoration treatments are effective at reversing mesophication: the replacement of flammable fuels of oaks and associated vegetation by less flammable fuels of mesophytic trees. Most tests of flammability have focused on comparisons of oak leaf litter with mesophyte leaf litter and have largely ignored the effects of grasses on flammability in these systems. Because restoration treatments frequently involve canopy thinning, which increases fire-adapted late-season grasses, efforts to increase flammability need to examine the role of grasses on reversing mesophication. In this study, we tested the effects of tree leaf litter and late-season grass litter on fuel consumption in the field during late growing season fires in restored and unrestored oak woodlands in north Mississippi (USA). We tested two hypotheses: 1) removing standing biomass and litter of late-season grasses significantly reduces fuel consumption by a late growing-season prescribed fire in a restored area with a significant late-season grass component (“graminification”), and 2) Removing tree leaf fuels reduces fuel consumption to a greater extent in areas in which oak leaf litter is a greater component of fuels than in areas in which mesophyte tree leaf litter fuels are abundant (mesophication).
Results/Conclusions
Consistent with the graminification hypothesis, removing litter of late-season grasses (Schizachyrium scoparium, Andropogon virginicus, and Saccharum giganteum) in a restored, oak-dominated woodland reduced fuel consumption. In addition, fuel consumption following the removal of tree leaf litter was greater in the area with a significant late-season grass component (the Restored area) than in areas lacking such grasses (Recently-Thinned and Untreated). Higher fuel consumption in the Restored area than in the Non-Restored areas largely occurred in locations where grass leaf area index was high. Consistent with the mesophication hypothesis, the removal of tree leaf fuels reduced fuel consumption to a greater extent in areas where tree leaf litter was dominated by pyrophytic oaks (i.e., Quercus stellata and Q. falcata; the Recently-Thinned and Restored areas) than in the area with a significant amount of mesophyte tree leaf litter (Untreated). Drying potential of tree leaf litter was greater in the Restored and Recently-Thinned areas than in the Untreated area. Results suggest that mesophication can be reversed by thinning mesophytes and opening the canopy, thereby increasing the ratio of oak to mesophyte/non-oak tree leaf surface litter. Increases in late-season grasses (graminification) at late stages of restoration may also increase flammability.
